Use secondary computer for rendering
Sheep-It! is a render farm service that is 100% free and works by using other people's computers to render your projects. It's a great service, and I would definitely recommend it. The only limitation with Sheep-It! is the 500mb project max size. If you don't want to or can't use Sheep-It!, I would recommend using this method:

Using  a cloud storage client

This works with any cloud storage solution that can be installed locally, such as Dropbox or OneDrive. For this example I'm using Google Drive.

First, sign up for a Google account, if you don't already have one.

Then, install Google Drive on both of your computers.
The Google Drive program essentially creates a physical location on your PC that stores everything on your Google Drive, and syncs it. For example, if you installed in on a PC with hard drive D:, and a laptop with hard drive F:. If you had google drive on both computers.. D:\Google Drive and F:\Google Drive would sync with each other.

Once you have google drive installed on both Computers, make sure you're signed in to it. Once that's done, simply create a folder on your Google Drive where all your frames in your animation will render.

Then, once you're ready to render, copy the project files over to your other PC.

Final step is to set your animation to render .PNGs, and set the render output directory to the folder you created earlier on your Google Drive.
Disable Overwrite and enable Placeholders.  



Then render animation, and when each frame is rendered, both computers will pick up on it and skip that frame, to begin working on the next one.